A power transmission device comprising a hydrodynamic rotation speed/torque converter and a bypass clutch, for instance, is anticipated from the document DE 44 33 256 A1. The power transmission device comprises an input that is connected non-rotatably with an engine. For instance, this is formed by housing with at least a wall extending more or less radially. The lock-up clutch disposed between the latter and the turbine wheel of the rotation speed/torque converter comprises at least a disc in rotary connection with the turbine wheel, which, on the one hand, can be brought into active connection with the housing and, on the other hand, with a piston that can be axially displaced and that is disposed between housing and turbine wheel, under the effect of hydraulic pressure on the latter. A chamber that can be pressurized in the first place with the hydraulic medium that serves for closing the clutch is provided between the piston and turbine wheel. A first chamber, for closing the lock-up clutch, which can be pressurized with the hydraulic medium, is provided between the piston and housing wall.
A second chamber, which can be pressurized with hydraulic medium, is provided between piston and turbine wheel, wherein this pressure chamber also comprises the impeller, stator and turbine wheel. Moreover, this pressure chamber is provided with two connections and cooling oil can circulate through this pressure chamber. In this way, in the first and second chamber to be pressurized with the hydraulic medium, means of reducing the rotation speed difference are provided between the prevailing low circulation rate of flow medium with an open or slipping lock-up clutch, in the dragging mode, inside the pressure chamber, between the turbine, piston and the higher circulation speed of the flow medium that prevails in the pressure chamber between the piston and housing. This is realized, for instance, by the radial-inward extension of the lock-up clutch discs with the blade-type form.
To improve the actuation of the lock-up clutch, means for the reduction of the rotation speed difference is known from DE 10 2006 028 557 A1, according to an embodiment in which the piston element of the actuation device of the lock-up clutch can be connected non-rotatably by means of a coupling spring device; however, it is movable in axial direction with the housing and features a flow-guide means that influences the rotation speed of the flow medium between the piston and the turbine wheel through which a rapid increase of the circulation speed of the flow medium should be targeted between the piston and the turbine wheel and hence the dynamic pressure at the beginning of the lock-up clutch actuation.
Generally, however, the problem exists in the application in vehicles, with regard to the ability to implement clean and jerk-free adjustment of the lock-up clutch, due to the hydrodynamic influences of flow media.